Toothbrush

Abstract

A toothbrush enables an appropriate brushing pressure and includes a sensing portion for sensing that an external force in a first direction orthogonal to the bristle tufting surface exceeds a predetermined value on a rear end side from the bristle tufting surface. The sensing portion changes a relationship between a displacement amount of the head portion when a load is applied to the head portion and a repulsive force generated according to the displacement amount from an increase to a decrease in the repulsive force at a first threshold value. The first threshold value relates to an increase in the displacement amount, and stops the decrease in the repulsive force at a second threshold value. The second threshold value relates to when the displacement amount is larger than the first threshold value.

1 . A toothbrush comprising:
 a head portion provided on a tip end side in a long axis direction and having a bristle tufting surface;   a grip portion disposed on a rear end side from the head portion; and   a neck portion disposed between the bristle tufting surface and the grip portion,   wherein a sensing portion for sensing that an external force in a first direction orthogonal to the bristle tufting surface exceeds a predetermined value is provided on a rear end side from the bristle tufting surface,   the sensing portion   changes a relationship between a displacement amount of the head portion when a load is applied to the head portion in the first direction toward a back surface side opposite to the bristle tufting surface and a repulsive force generated according to the displacement amount from an increase to a decrease in the repulsive force at a first threshold value according to an increase in the displacement amount, and   stops the decrease in the repulsive force at a second threshold value where the displacement amount is larger than the first threshold value, and   when the repulsive force when the displacement amount is at the first threshold value is A, and the repulsive force when the displacement amount is at the second threshold value is B,   a value represented by B/A is 0.3 or more and 0.9 or less.   
     
     
         2 . The toothbrush according to  claim 1 ,
 wherein the repulsive force A is 1.0 N or more and 5.0 N or less.   
     
     
         3 . The toothbrush according to  claim 1 ,
 wherein, when the displacement amount at the first threshold value is C and the displacement amount at the second threshold value is D,   a value represented by D−C is 0 mm or more and 1.5 mm or less.   
     
     
         4 . The toothbrush according to  claim 3 ,
 wherein the displacement amount C is 28 mm or less.   
     
     
         5 . The toothbrush according to  claim 1 ,
 wherein, when the displacement amount exceeds the second threshold value, the sensing portion causes the repulsive force to increase according to the increase in the displacement amount.   
     
     
         6 . The toothbrush according to  claim 5 ,
 wherein, starting from the displacement amount at the second threshold value, a rate of increase in the repulsive force until the displacement amount of the head portion reaches 4 mm is 0.015 or more.   
     
     
         7 . The toothbrush according to  claim 1 ,
 wherein, in the sensing portion,   when a load is applied to the back surface side to stop at least the decrease in the repulsive force and thereafter the load is released, a relationship between the displacement amount and the repulsive force after the release remains the same as before the load is applied.   
     
     
         8 . The toothbrush according to  claim 1 ,
 wherein the sensing portion includes   a reversal portion that connects a first region on the tip end side from the sensing portion and a second region on the rear end side from the sensing portion, and that snaps, buckles, and reverses as the head portion is displaced to the back surface side opposite to the bristle tufting surface in the first direction due to the external force exceeding the threshold value, and   an elastic deformation portion that is disposed with a gap from the reversal portion, connects the first region and the second region, and elastically deforms at least up to the external force at which the reversal portion snaps, buckles, and reverses, and   the reversal portion is located between an outer contour on the bristle tufting surface side and an outer contour on the back surface side in the elastic deformation portion in a side view viewed in a direction orthogonal to the long axis direction and the first direction.   
     
     
         9 . The toothbrush according to  claim 8 ,
 wherein a path where the elastic deformation portion is deformed due to the external force in the first direction and a path where the reversal portion is deformed due to the external force in the first direction are provided in a non-interfering manner.   
     
     
         10 . The toothbrush according to  claim 8 ,
 wherein the elastic deformation portion and the reversal portion are disposed with a gap in a second direction orthogonal to the first direction and the long axis direction.   
     
     
         11 . The toothbrush according to  claim 10 ,
 wherein the gap is a through-hole extending in the first direction.   
     
     
         12 . The toothbrush according to  claim 10 ,
 wherein the reversal portion has a protrusion shape toward the back surface side when the external force in the first direction is equal to or less than the predetermined value, and is reversed in a protrusion shape toward the bristle tufting surface side when the external force in the first direction exceeds the predetermined value.   
     
     
         13 . The toothbrush according to  claim 12 ,
 wherein the reversal portion includes a groove portion extending in the second direction on at least one of the bristle tufting surface side and the back surface side in a region including an apex of the protrusion shape.   
     
     
         14 . The toothbrush according to  claim 8 ,
 wherein the reversal portion is made of a hard resin, and   a portion of the elastic deformation portion is made of a resin having a hardness different from that of the hard resin.